1. Field of the Invention
The present invention relates to absorption technique capable of easily and reliably absorbing water formed in a fuel cell. More specifically, it relates to a fuel cell cartridge capable of absorbing water formed in a power generation part of a fuel cell, a fuel cell system comprising the fuel cell cartridge, an electrical apparatus comprising the fuel cell system, and a method for recovering water formed in a fuel cell system.
2. Description of the Related Art
Portable information-processing apparatuses such as mobile phones and portable computer systems (notebook personal computers) have been more and more miniaturized, reduced in weight, increased in speed and improved in function. Thus, cells serving as power supplies thereof have been more and more miniaturized, reduced in weight and increased in capacity.
Most popular drive power supplies in the portable information-processing apparatuses are lithium-ion cells. The lithium-ion cells have had a high drive voltage and a high cell capacity from their launch in market, and their performances have been improved along the progress of mobile phone apparatuses.
Improvements in the performances of the lithium-ion cells, however, have some limitations, the lithium-ion cells become to fail to satisfactorily meet the requirements as the drive power supplies of such high-function portable information-processing apparatuses.
Under these circumstances, noble energy devices as alternatives for the lithium-ion cells have been developed. Among them, fuel cells have received attention. These fuel cells can generate electric power by supplying a fuel to an anode to thereby generate electrons and protons, and allowing the protons to react with oxygen supplied to a cathode.
A key feature of the fuel cells is that the fuel is supplied to the anode and oxygen is supplied to the cathode. The fuel cells can thereby generate electric power over a long time by supplying the fuel and the oxygen. They can be applied as power supplies for equipment as in secondary cells (rechargeable batteries), except for supplying the fuel instead of charging in the secondary cells. In addition, fuel cells using methanol as the fuel have a theoretical energy density in terms of active material about ten times higher than that of the lithium-ion cells and can significantly contribute to miniaturization and weight reduction. Accordingly, attempts have been increasingly made to use such fuel cells not only as dispersed power sources and large-size power generators for electric-powered vehicles but also as subminiature power generating units in portable information-processing apparatuses such as notebook personal computers and mobile phones.
In the field of miniature fuel cells, “direct methanol fuel cells” using an aqueous methanol solution as the fuel have been increasingly researched and developed. Unit cells of the direct methanol fuel cells each generally have a fuel electrode, a solid electrolyte, an air electrode, and current collectors arranged so as to sandwich these components.
In the direct methanol fuel cells, water is generated according to the following mechanisms (1), (2) and (3) upon an electric power generation reaction of methanol serving as the fuel. Initially, (1) methanol as the fuel reacts with water (electric power generation reaction) to yield carbon dioxide and H+s (protons) according to the following formula: CH3OH(fuel)+H2O→CO2 (emitted from the fuel electrode)+6H++6e−. Next, (2) the H+s(protons) in the solid electrolyte migrate from the fuel electrode to the air electrode (proton conduction) to yield an inward current in the fuel cell. Next, (3) the protons are oxidized in the air electrode to yield water according to the following formula: 6H++3/2O2+6e−→3H2O. As is described above, water is generated typically by the electric power generation reaction in the air electrode. When comes in contact with an atmosphere at relatively low temperatures surrounding the fuel cells or with an article at relatively low temperatures, the air containing the water undergoes condensation in the air or upon a surface of the article.
However, such condensed water coming into the inside of an apparatus to be powered by the fuel cells may invite malfunctions or defects in the apparatus and uncomfortable wet conditions to a user. Thus, the fuel cells preferably have a structure and/or function to avoid the water from discharging to outside.
A conventional example of the structure and/or function to avoid the water from discharging to outside is a space (chamber) for recovering and reserving the water in a fuel cell cartridge (Japanese Patent Application Laid-Open (JP-A) No. 2003-92128 and JP-A No. 2003-203668).
According to this technique, however, the fuel cell cartridge has a complicated structure and/or mechanism, requires higher production cost and exhibits a poor handleability. The recovered and retained water is not easily disposed, and the apparatus exhibits poor recycling efficiency. In addition, the presence or absence of water absorption is not easily detected.
Accordingly, an object of the present invention is to provide a fuel cell cartridge that has a simple structure and/or mechanism, does not require high production cost, exhibits satisfactory handleability, can easily and reliably recover the water formed in the fuel-cell power generation part, can easily dispose of the recovered water upon the recharge of the fuel, is easily recyclable and exhibits good recycling efficiency and environmental friendliness.
Another object of the present invention is to provide a fuel cell system that includes the fuel cell cartridge, has a simple structure and/or mechanism, does not require high production cost, exhibits satisfactory handleability, can easily and reliably recover the water formed in the fuel-cell power generation part, can easily dispose of the recovered water upon the recharge of the fuel, is easily recyclable and exhibits good recycling efficiency and environmental friendliness.
Yet another object of the present invention is to provide an electrical apparatus that includes the fuel cell system, can be driven by using clean energy derived from the fuel cell system, can easily and reliably absorb water formed in the fuel cell system without leakage of water inside or outside the apparatus, exhibit satisfactory handleability and can easily dispose of the recovered and retained water.
Another object of the present invention is to provide a method for easily and reliably recovering water formed in a fuel cell system.